18 REPORT 1865. 



different parts of her surface would not attain the same degree of heat. Nearly 

 two-thirds of the hemisphere turned towards us is honeycombed with gigantic 

 craters, and covered with the debris of stupendous volcanic eruptions, the region in 

 which Tycho is situated forming a principal part of the whole extent,_ and being 

 conspicuous to the naked eye from its superior brightness. That region should 

 therefore absorb less heat in proportion to its reflecting properties. On the other 

 hand, the dark surfaces of the moon would absorb and radiate heat in the inverse 

 ratio to their non-reflecting properties. The above facts must be borne in mind in 

 considering the question of the heat attained by the moon at the periods of oppo- 

 sition and quadrature. In addition to this, though the whole surface of the moon 

 is exposed in turn for from about thirteen to rather more than sixteen days to the 

 solar rays, in speaking of the heat which our satellite attains it must not be con- 

 sidered that equal surfaces illuminated— e. r/., at the first and third quarters— are 

 equally heated because so illuminated, or without reference to the duration of the sun's 

 radiation upon them. On the contrary, at the day of first quarter, the region of the 

 moon which has received the rays of the sun for a mean period of rather more than 

 four days, after being subjected* to the most intense cold during the moon's long 

 night, has been but very little warmed up to the completion of the first quarter ; 

 the region opposite the earth having received the heat of the sun's rays for only 

 about four-and-twenty hours— a period manifestly insufficient for any surplus heat 

 to have been absorbed, even if the region had been favourable for storing radiant 

 heat. At the period of last quarter, on the other hand, the surface illuminated 

 will have been heated thrice as long as at the first quarter, namely, for a mean 

 duration of eleven days ; and not only so, but at the time when the moon com- 

 pletes her third or "last quarter," a similar surface to that at first quarter will have 

 received the heat of the sun's rays for 360 in place of 24 hours, — with this additional 

 peculiarity, that the surface generally will be a good absorber of heat. The heat 

 of the moon at the last quarter might, on like grounds, be shown to be greater, or 

 certainly not less, than at the full. It will be sufficient, however, to point out that 

 the portion of the moon's fully-illuminated hemisphere opposite to us, and which 

 radiates heat directly towards the earth, is not heated so intensely at the full as at 

 the last quarter, or for a day or so after that phase ; the ratio in favour of the 

 latter period being nearly two to one, whilst the ratio in favour of the last quarter, 

 compared with a corresponding region in the first quarter, is rather more than 

 fifteen to one ; the measure being the duration of solar radiation, without reference 

 to the dark or light surfaces on which it falls. 



The author exhibited a curve of the mean temperature at Greenwich for fifty 

 years*, showing that the period of the greatest heat of the lunar surface synchro- 

 iiized with the period of greatest [average] monthly cold in the terrestrial atmo- 

 sphere, and conversely. 



On the Self-Registering Barometer at the Liverpool Observatory. 

 By Alfeed King, M.I.C.E. 

 The increased attention given of late to meteorological observations has naturally 

 created a demand for instruments, which, by their own action, shall produce' a 

 permanent record of the various phenomena of our atmosphere. Photography 

 requires considerable skill in the manipulation, and a more direct and simple mode 

 of self-registration is therefore in some cases a desideratum. The instrument de- 

 scribed in this paper is & floating barometer, constructed by Mr. King, since the 

 exhibition of the first trial instrument at a former Meeting of the British Associa- 

 tion in 1854. In the ordinary barometer the variations in the atmospheric pres- 

 sure are indicated by the varying height of a column of mercury within a tube ; in 

 this floating barometer they are made evident by the movements of the tube itself, 

 which is counterpoised by a weight, say at 29 inches. If by the increase in atmo- 

 spheric pressure the length of the column of mercury in it is increased to 80 

 inches, it is evident the equilibrium will he destroyed, and the weight of the 

 additional inch of mercury will cause the tube to descend. If, on the other hand, 

 the pressure is reduced to 28 inches, one inch of mercury in the column will be lost, 



* See curve for 43 years, Eeport 1859. 



